How to Defend Against JavaScript Malware

For several quarters in a row, malicious JavaScript has made up a significant portion of the malware blocked by WatchGuard’s Firebox UTM appliances according to our Internet Security Report. As a matter of fact, several of the top ten most common malware strains are written in JavaScript. To help organizations better understand how JavaScript malware works, and how organizations can defend against it, Marc Laliberte, one of WatchGuard’s Threat Analysts, recently wrote a column for Third Certainty on this topic.

In the article, he looks at why firewalls detect so much JavaScript malware, and explains that hackers often use JavaScript to write “droppers.” These programs infect a target system and then download and execute the actual malware payload onto that system. While these are fairly easy to detect, hackers often obfuscate their code to make these droppers unreadable to signature-based detection solutions. Fortunately, defending against JavaScript droppers is straightforward. Here’s an excerpt from Marc’s article explaining how user education can help stop JavaScript malware.

“Fortunately, (obfuscated JavaScript droppers) can be defeated with a little bit of user education. All droppers require interaction from the would-be victim. The user must run the script by clicking it for it to do damage. Training users to be suspicious of email attachments, especially unsolicited ones, can go a long way toward protecting you and your organization from JavaScript-based malware.”

Marc also notes that a layered security approach can help protect your system. In addition, anti-spam solutions and both behavior-based and signature-based malware detection solutions contribute to helping keep a target system safe. Using them all together will create a strong defense against JavaScript malware.